docs(migration): state how to register components in content folder…

… as global components (#2935)

docs/content/docs/1.getting-started/4.migration.md

@@ -30,6 +30,7 @@ Don't worry, you don't need to modify your content files. We made sure that Cont
 - We consolidated the `ProsePre`, `ProseCode`, and `ProseCodeInline` components
   - `ProseCodeInline` is now `ProseCode`
   - `ProseCode` is now `ProsePre`
+- Components created under the `components/content` directory are no longer automatically registered as global components. If you use [dynamic rendering](https://vuejs.org/guide/essentials/component-basics.html#dynamic-components) to render these components outside markdown files, you must manually register them in your Nuxt app. Check out the [Nuxt - Custom Components Directories](https://nuxt.com/docs/guide/directory-structure/components#custom-directories) documentation for more information on how to do so.
 
 ### General Changes